Recently, blood pressure monitors have come into wide use in, for example, not only hospitals but also general households for the purpose of health care. The blood pressure monitors for the general households are typically automatic blood pressure monitors that are easy to operate.
Automatic blood pressure monitors based on various measurement methods and configurations have been developed, and an oscillometric electronic blood pressure monitor is one of such blood pressure monitors. This oscillometric electronic blood pressure monitor detects a pulse wave superposed on cuff pressure, and calculates a blood pressure on the basis of changes in the amplitude of the pulse wave.
As shown in FIG. 5, the above-mentioned oscillometric electronic blood pressure monitor 100 includes a cuff 110, a pressure sensor 113, a pump 114, an exhaust valve 115, an information processing unit 120, an operation switch 121 and a display 122. The cuff 110 has an air bag 111 and a core 112. The pressure sensor 113, the pump 114 and the exhaust valve 115 are in communication with the air bag 111 through a tube 116. The information processing unit 120 is connected to the pressure sensor 113, the pump 114 and the exhaust valve 115. The operation switch 121 and the display 122 are connected to the information processing unit 120.
During a blood pressure measurement, the cuff 110 is attached to the upper arm in a rolled condition where one end of the cuff is wound within the other end thereof. Further, a pressure signal is input to the information processing unit 120 from the pressure sensor 113 via a filter and an A/D converter (not shown), and the information processing unit 120 controls the pump 114 and the exhaust valve 115.
As shown in FIG. 6, in the oscillometric electronic blood pressure monitor 100, the cuff pressure is first elevated to a proper pressure value. Then, in the process of gradual reduction of the cuff pressure, the oscillometric electronic blood pressure monitor 100 measures a systolic blood pressure (maximum blood pressure) and a diastolic blood pressure (minimum blood pressure). At this moment, a change pattern (pulse wave envelope) of the pulse wave amplitude is required in an oscillometric method. This pulse wave envelope includes a point S corresponding to the systolic blood pressure, the maximum (point P) of the pulse wave amplitude and a point D corresponding to the diastolic blood pressure.
That is, the oscillometric electronic blood pressure monitor 100 has to previously elevate the pressure to the S point or more before the start of measurement operation. If the pressure is not elevated to the S point or more (elevation of the pressure to the proper pressure value), the S point is absent at the point of detection of the point P in the blood pressure measurement operation. In this case, the systolic blood pressure (maximum blood pressure) cannot be calculated, resulting in a measurement error.